Transvenous endocardial leads may be placed inside a chamber of a patient's heart by passing the lead through a venous entry site, such as the subclavian vein or the cephalic vein, or a tributary thereof, along a venous pathway into the superior vena cava and into the right cardiac chambers. Cardiac vein leads may be advanced further, from the right atrium through the coronary sinus ostium into the coronary sinus and ultimately into one of the various cardiac veins for stimulation and/or sensing of the left heart chambers.
Cardiac lead placement is important in achieving proper stimulation or accurate sensing at a desired cardiac location. Endocardial or cardiac vein leads are generally implanted with the use of a guide catheter or a guidewire or stylet to achieve proper placement of the lead. Cardiac leads generally need to be highly flexible in order to withstand flexing motion caused the beating heart without fracturing. A stiff guidewire or stylet provides a flexible lead with the stiffness needed to advance the lead through a venous pathway. During an implantation procedure, the stylet or guidewire may be removed and replaced by a stylet or guidewire having a different curvature at its distal end to allow the physician to steer the lead through variable curves and branches encountered along a venous pathway. Repeated withdrawal and reinsertion of a stylet or guidewire, however, can be time consuming, increase the risk of infection, and increase the risk of damaging the lead or a blood vessel. Multiple stylets or guidewires having differently sized curvatures at the distal end may be required during a single implant procedure, increasing the number of steps and time involved in implanting a lead.
Guide catheters may also be used to guide the implantation of a medical lead, or various other medical devices, such as angioplasty balloon catheters, ablation catheters, electrophysiological diagnostic catheters, or other devices. Some catheters, particularly electrophysiological diagnostic catheters, may be provided with steering mechanisms that allow the distal end of the catheter to be bent or curved in a desired direction to overcome an obstacle. One mechanism for controlling the curvature or bend applied to the distal end of a catheter includes the use a pull wire. A pull wire is generally attached to a point at the distal end of the catheter such that when traction is applied to the pull wire, the distal end of the catheter is caused to curve or bend. A steerable stylet and manipulative handle assembly, which includes a traction element or pull wire, for guiding a lead or a catheter to a desired location is disclosed in U.S. Pat. No. 5,396,902 issued to Brennen, et al. An electrophysiology catheter assembly which uses a single core wire to cause the tip section of the catheter to deflect is disclosed in U.S. Pat. No. 5,807,249 issued to Qin, et al.
A guide catheter is generally required to possess a certain amount of stiffness to allow the guide catheter to be advanced through body vessels or cavities, yet the guide catheter must be flexible enough to maneuver around obstacles or through a tortuous pathway. Compromise between these design requirements may be met by providing guide catheters having variable stiffness along their length. Greater flexibility near the distal end of a catheter allows the distal end to be more easily maneuvered. A variable stiffness balloon catheter is disclosed in U.S. Pat. No. 6,322,534, issued to Shkolnik, wherein a relatively stiff shaft portion is reinforced with a braided layer and a more flexible distal portion is reinforced with a single helical wire coil. A dilation catheter with a stiffening wire having at least two stepped diameter reductions along its length to vary stiffness from a stiff proximal end to a less stiff distal end is disclosed in U.S. Pat. No. 6,030,405 issued to Zarbatany et al. Variation in stiffness and curvature of a guide catheter tip section may also be accomplished using a temperature-activated memory material such as nitinol. Shape memory elements for controlling steering and/or stiffness of medical devices, such as guide catheters, are disclosed in U.S. Pat. No. 5,531,685 issued to Hemmer et al.
In one prior art method for implanting a cardiac vein lead, a steerable electrophysiology diagnostic catheter is advanced through a guide catheter and used to steer the guide catheter into the coronary sinus. The diagnostic catheter is then removed from the guide catheter and a lead is advanced through the guide catheter into the coronary sinus. Because the size of the guide catheter that can accommodate a steerable diagnostic catheter is generally too large to be advanced further into the deeper coronary veins, a stylet or guidewire is inserted through a lumen of the lead to provide the lead with stiffness needed to advance the lead through the cardiac veins. This procedure involves the use of several different instruments, requires considerable skill, and is generally time-consuming.
In regard to cardiac lead applications, therefore, it is desirable to provide a guide catheter and medical lead system that may be of a reduced size to allow advancement into narrow blood vessels, in particular into the cardiac veins. A cardiac vein lead having a reduced outer diameter that may include a flexible tip is disclosed in U.S. Pat. No. 5,935,160 issued to Auricchio et al. The methods for implanting the cardiac vein lead, however, may still require the use of a guide catheter and/or a guidewire or stylet and the additional steps associated with placing and removing a guidewire or stylet. It is desirable, therefore, to provide a system for dynamically steering a small diameter guide catheter and lead to a desired location without the need for guidewires or stylets, thereby simplifying the implantation procedure and reducing the procedure time.